1. Field of the Invention
The present invention relates to a method of mounting a light emitting element, such as a semiconductor laser element, a light emitting diode or the like, which is formed on a transparent substrate. More particularly, the present invention relates to a method of positioning and mounting a light emitting element on a mounting member so that a light emission point of the light emitting element is accurately positioned at a predetermined position.
2. Description of Related Art
Conventionally, in a light emitting device such as a semiconductor laser device, a light emitting diode and the like, a light emitting element in the form of a chip is relatively small. In order to protect the element from external force and because of its mounting procedure and its usage, it is usually mounted on an apparatus after mounted on a holder member or a mounting member larger than the light emitting element itself. Also, since the light emitting device is a heat generator, it is necessary to radiate the heat generated therefrom.
For those reasons, the light emitting device is used in a condition that the light emitting element thereof is mounted on a mounting member such as a sub mount, a heat sink or the like, in many cases.
Conventionally, when the light emitting element is mounted on a mounting surface of a necessary mounting member, for example, on a mounting surface of a heat sink, a sub mount, an LOP (Laser On Photodiode) or the like, an outer contour of the light emitting element or an electrode pattern or a marker put on the light emitting element is used as a reference point or a reference line. The light emitting element is visually position-matched with the reference position of the mounting member and fixed thereon. For example, a cross-shaped marker is put on a side of a laser stripe of the light emitting element, and this is used as the reference point.
Here, a conventional method of mounting a light emitting element is explained by exemplifying an operation for mounting a light emitting element on a heat sink. First, the configuration of a mounting apparatus used when a semiconductor laser element is mounted is described with reference to FIG. 5. A mounting apparatus 10 comprises a position-matching stage (hereafter, referred to as a matching stage) 12 having an X-Y plane, a feeding collet 14 and an image sensor 16, as shown in FIG. 5.
The matching stage 12 is placed at a position separated by a predetermined distance in a predetermined azimuth with respect to a heat sink (not shown) on which a semiconductor laser element C is mounted. The feeding collet 14 sucks and holds the semiconductor laser element C, one by one, from a tray or sheet 18 on which a plurality of chip-shaped semiconductor laser elements C are aligned, and then feeds to and places it on the matching stage 12.
Moreover, while sucking and holding the semiconductor laser element C on the matching stage 12, the feeding collet 14 is driven by a driving mechanism (not shown) and freely moved in an X-direction, a Y-direction and a θ-azimuth on the matching stage 12 to thereby adjust the position and the azimuth of the semiconductor laser element C.
The image sensor 16 is, for example, a CCD camera. It recognizes the marker put on the semiconductor laser element C or the outer contour thereof, and detects displacement in the azimuth θ and in the position on the X-Y plane of the semiconductor laser element C from the reference line and the reference point on the X-Y plane of the matching stage 12.
Next, the image sensor 16 sends the displacement information of the azimuth and the position to the driving mechanism of the feeding collet 14, and the feeding collet 14 is driven to correctly adjust the azimuth and the position of the semiconductor laser element C on the matching stage 12.
The feeding collet 14 sucks the semiconductor laser element C after the displacement in the azimuth and in the position are eliminated, and moves it by a predetermined distance in a predetermined direction, and then places it on the mounting member.
The method of mounting the semiconductor laser element C on the heat sink using the mounting apparatus 10 will be described below with reference to FIG. 5. First, the semiconductor laser element C is picked up, one by one, from the tray or sheet 18, on which the plurality of chip-shaped semiconductor laser elements C are aligned, using the feeding collet 14, and then fed to and placed on the matching stage 12.
Next, displacement of the semiconductor laser element C from the reference lines on the matching stage 12, namely, the displacement in the X-direction and the Y-direction (hereinafter, referred to as “linear displacement”), and displacement in the rotational direction within the X-Y plane, namely, the azimuth (θ) (hereinafter, referred to as “angular displacement”), are measured by measuring the marker put on the semiconductor laser element C or the outer contour of the semiconductor laser element C through the image sensor 16.
In accordance with the measured linear displacement in the X-direction and the Y-direction and the measured angular displacement of the rotational direction (θ) within the X-Y plane, a control signal is outputted to a driving mechanism (not shown) of the feeding collet 14, and the feeding collet 14 is driven to thereby correctly adjust the position of the semiconductor laser element C on the matching stage 12.
Next, the semiconductor laser element C after the adjustment in the position and the azimuth is held by the feeding collet 14, and fed to a mounting surface of the heat sink (not shown). The heat sink for mounting the semiconductor laser element C is positioned in advance at a position separated in a predetermined azimuth by a predetermined distance from the matching stage 12. Thus, the semiconductor laser element C is accurately positioned in the condition that it is fed to the mounting surface of the heat sink. Subsequently, the semiconductor laser element C is fixed on the heat sink.
The most important condition when a semiconductor laser element is positioned on a mounting member such as a heat sink or the like is to accurately position the light emission point of the semiconductor laser element with respect to the mounting member.
However, in view of this, the above-mentioned conventional method of mounting the light emitting element has the following problems.
Firstly, when the semiconductor laser element is position-matched using the matching marker put on the semiconductor laser element as a reference, it is not possible to position the light emission point of the semiconductor laser element with respect to the heat sink at high accuracy if the positioning accuracy between the light emission point of the semiconductor laser element and the marker is insufficient. Actually, it is very difficult to precisely position the marker with respect to the light emission point. Thus, it has been difficult to improve the positioning accuracy of the semiconductor laser element.
When the marker is put on the semiconductor laser element, if the laser stripe and the marker can be formed using a single mask as the mask to form the laser stripe, it is possible to form the marker at high accuracy with respect to the laser stripe. However, it is not always easy practically. Moreover, even if the marker and the laser stripe are formed using the single mask, there may be a case that a marker pattern is broken. Under the above-mentioned situation, it is difficult to position-match the light emission point with the mounting member at high accuracy and then mount the semiconductor laser element on the mounting member.
Even if the marker is put on the semiconductor laser element, in a case where the semiconductor laser element is mounted on the heat sink with reference to a marker of a sub mount after a semiconductor laser element chip is once mounted on the sub mount, it is not possible to mount the semiconductor laser element at high accuracy.
Secondly, the shape and the dimensions of the outer contour of the semiconductor laser element cannot be accurately adjusted. Thus, even if the outer contour of the semiconductor laser element is used as the reference so as to match with the mounting member, it is difficult to improve the positioning accuracy of the light emission point of the semiconductor laser element with respect to the mounting member. In particular, in a case of a GaN-based semiconductor laser element formed on a sapphire substrate, when a number of semiconductor laser elements formed on a wafer are made into chips, cleavability of the wafer is poor. Thus, it is difficult to cleave the wafer and make it into chips. Hence, an etching process, a dicing process and the like are used for making the wafer into the chips. Consequently, the outer contour of the chip is deviated from a predetermined contour, in many cases. Hence, the positioning accuracy becomes poor when the outer contour of the chip is used as the reference to thereby position-match with the mounting member.
Thirdly, there is also a problem that it takes a long time to position-match the semiconductor laser elements.
In the above-mentioned explanation, the problems have been explained by exemplifying the semiconductor laser element. However, those problems are pointed out even in a case of the light emitting diode. That is, these problems are pertinent generally to the light emitting elements.